Since filling tanks on more humid
days helps reduce the risk of static,
perhaps spraying the interior of the
balloon with water and detergent
solution to increase its internal
humidity level could be a smart idea.
Those around the balloon should
wear gloves, long sleeve shirts, and
head cover with goggles or a face
shield. Since hydrogen burns fast and
upward, filling crews around and
below the balloon need protection.
In the old days, people around
tanks of hydrogen swept a straw
broom around them to locate possible
burning hydrogen leaks. Today, we
use IR thermometers to detect the
invisible flames of burning hydrogen.
Since they are so inexpensive these
days, every near space group using
hydrogen should carry at least one.
THE FAA
The last speaker was Veronica
Bailey of the FAA (Federal Aviation
Administration). A 22-year career
employee, her expertise is in education
these days. Veronica manages air shows
and career fairs for the FAA. She also
partners with CAP, ROTC, Project Lead
the Way, Boys and Girls Clubs, and
some universities with aviation programs.
One especially interesting thing she
talked about is that the FAA is about
to face a shortage. There are too
many employees nearing retirement
age and the agency is looking to hire
NOTE: All PCB patterns and files
are available on the Nuts & Volts
website at www.nutsvolts.com.
5,000 new employees a year for
the next five years — just to replace
retiring traffic controllers. This sounds
like a career opportunity to me!
This concluded Friday’s presentation,
after which Near Space Ventures gave
the audience a weather briefing for
Saturday’s flights. If you’d like to view
some of the activities from this day,
go to nearsys.com > Amateur Radio
High Altitude Ballooning > Data from
Past Flights > 2008 > NearSys 08A for
a complete mission report and video.
Onwards and Upwards,
Your near space guide
NV
REEFING PARACHUTES
I do want to mention reefing parachutes this month.
Reefing prevents a parachute from fully opening at high
altitude. Then, once it has descended to a lower altitude,
the parachute is allowed to fully open. A reefed parachute
lets the near spacecraft descend faster early in the recovery
while it’s at high altitude and not a hazard to those on the
ground. Then, when near touch-down, the parachute
completely opens, slowing the near spacecraft to a safe
landing speed. A quick drop from high altitude prevents
the near spacecraft from drifting quite as far and puts the
recovery zone closer to the launch site. The reefing concept
I describe is actually untested; however, it should work well
in near space applications.
Using a 2N3904 NPN transistor allows a low power
source like the piezo alarm of an inexpensive stop watch to
trigger the line cutter. To modify a stop watch for this
purpose, you’ll have to open it up and remove the piezo
element of its alarm. The piezo element should drop right out,
exposing the two springs used to make electrical contact with
it. Solder wires to both springs. (I found inserting a bared
wire into the spring is a great way to make the connection.)
Then, set the alarm and measure the polarity of the wires
when the alarm beeps. You need to identify which is positive
and which is negative. The positive wire attaches to the left
side of the line cutter PCB, at the pad marked signal. The
negative wire attaches to the pad marked ground. The relay in
this design is a five volt RadioShack reed relay, so the line
cutter needs four cells, or six volts to operate. Alternatively,
the line cutter’s three wire cable could connect to a
microcontroller project board like the Parallax Homework
board. A separate battery provides the power for the
nichrome line cutter.
That cable is the two
wires on the right side
of the PCB.
The reefing line is
■ The line cutter
suitable for control by a
variety of devices that
was used successfully
in the past to terminate
two near space flights.
80
February 2009
made by threading Spectra kite line
through all eight twill tape loops at
the bottom of the parachute canopy
and the nichrome coil of the line
cutter. I think it might be beneficial
to add additional twill loops to
the edge of the canopy. Having
additional loops for the reefing line
to pass through will more fully
restrict the opening of the
parachute. The Spectra kite line is
then tied to form a loop smaller
than the diameter of the fully
opened parachute. Now when the
balloon bursts, the reefing line will
prevent the parachute from opening
fully. The partially opened parachute
still creates drag, but not to the
extent that it would fully opened.
Then at some later time, a stop
watch alarm or a microcontroller
triggers the line cutter and it melts
the reefing line. This then allows the
parachute to fully open.
■ Parts placement
for the line cutter.
Now, to mount the line cutter. I’ve attached line cutters,
batteries, and a timer to the apex of the parachute with no
ill effects. I believe the battery and timer for the line cutter
should be mounted there and the line cutter be allowed to
dangle down the side of the canopy. To restrict the movement
of the line cutter and its wires, a few small twill tapes should
be sewn to the canopy to form a restraint. Sewing a cloth
tunnel down the canopy in place of a couple of twill loops is
probably too much trouble and overkill.
You’ll find a ton more information on parachute design
in the book, Parachute
Recovery Systems, by T. W.
Knacke. There’s so much
knowledge packed into this
book that I’ve barely begun
to scratch the surface.
■ The first test of a
reefed parachute.
Eventually, this system
will be tested over the
skies of Kansas.
